Adding odd numbers will only give you an even sum if the amount of numbers you added is an even number.
For example,
25 is an odd number. If you add 25, 2 times (2 is an even number) you will get 50 (an even number). If you add 25, 4 times (4 is an even number) you will get 100 (still, an even number)
However, if you add 25, 3 times (an odd number) you will get 75 (an odd number). If you add 25, 5 times (an odd number) you will get 125 (still an odd number).
Hopefully, that helped (: Sorry if I confused you lol